Air is usually added to tires by a repeated series of checks on the tire pressure in alternation with additions of air to the tire followed eventually by a bleeding of any excess air from the tire. Overinflation of tires has caused accidents due to the impossibility of making accurate pressure measurements during the tire filling process.
Gauges for routine daily measurement of tire air pressure to maximize vehicle safety and tire performance often may not be left on the tire during use of vehicle or are difficult to read to the type of pressure indicator or the angle or projection of the gauge from the tire. Most of the gauges now used are not visible to the operator of the vehicle at least half of the time due to the position of the dial face and the dial when the rotation of the tire ceases. In addition, gauges using liquid barometer pressure devices often are difficult to read after operation of the vehicle, even at slow speeds, due to foaming of the liquid in the gauge during rotation of the tires.